Paralell Bridging Tandberg 3006a to Mono? - diyAudio
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Old 7th September 2012, 02:08 AM   #1
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Default Paralell Bridging Tandberg 3006a to Mono?

Can I parallel bridge my 3006a to mono (parallel)? The grounds are common for both channels. Observing schematics on line it also looks like the 3009 mono amp is exactly that. Please advise.
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Old 7th September 2012, 11:39 AM   #2
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You can find the schematics at Index of /tandberg

Once again thankyou for your help.
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Old 7th September 2012, 11:00 PM   #3
amptech is offline amptech  Scotland
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Bridging an amplifier can be done two ways 1 using a opamp circuit or 2 via a resistor from the feed back path of the tail pair transistors this idea as been done by so many brand name amplifiers such as peavey/ h/h etc...

For more info try rod Elliot sound page and follow the bridging project.
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Old 9th September 2012, 11:53 AM   #4
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Parallel bridging (for low impedance loads) requires disconnecting the front end of one channel and connecting the gate drives to the other channel (the gray and green wires), then you connect the white output wire to the other channel's white wire.
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Old 9th September 2012, 11:56 AM   #5
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can't I just combine the inputs?
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Old 9th September 2012, 12:22 PM   #6
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"can't I just combine the inputs? "

Absolutely not.

Any difference in channel gain and DC off-set will cause a 'tractor-pull ' situation.

http://www.ti.com/lit/an/snaa021a/snaa021a.pdf

Notice in 6.2.1 how the gain setting resistors are all 0.1% and that the outputs are summed through 0.1Ω resistors?

I think it might be easier to do it the way Tandberg does it (as described in my earlier post).
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Last edited by djk; 9th September 2012 at 12:31 PM.
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Old 9th September 2012, 02:36 PM   #7
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Thank you, I understand. You saved me a lot of problems.
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Old 9th September 2012, 05:44 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

Parallel is not bridging. Bridging requires common ground. Stereo amplifiers
that are already bridged can be paralleled via small output resistors to
absorb DC offset and slight gain differences, same with non bridged.

So yes you can just parallel the inputs and connect the outputs together
via small resistors, but I'm having trouble seeing a useful scenario for
this. Stereo power amplifiers in my book inevitably end up being
relatively poor value if wired as parallel mono blocks.

A good 4 ohm stereo amp bridged into 8 ohm is a very different matter.

rgds, sreten.
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Old 9th September 2012, 06:07 PM   #9
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My intent is to improve the amplifiers's perfromance into low impedance. The Tandberg is rated for 8-16 ohms. I am using two amps (biamp now) each into a speaker having an impedance of 4-6 ohms. If it is easy I wanted to try it and see if there is any difference. Resistors would make this very easy. Around 0.1 ohm? Or, I am seriosly thinking about driving only one input stage as sugested above, but I will have to make some connectors to do this. I want to be able to come back to the original configuration if there is no sonic gain.

Thank You everyone for some great advise.
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Old 21st September 2012, 09:04 PM   #10
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There was a factory kit for bridging the 3006A (and others). It's a small board that mounts inside and wires to one of the front end boards. Basically just inverts the signal going to that channel. IIRC, the schematic is available... should have a copy at home.

The output stages are common (-) so once the bridging adapter is in place, you just use the two (+) outputs to drive the load. Probably shouldn't bridge it into loads below 8 ohms however.

John
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